1. Field of the Invention
The present invention relates to a rolled recording paper setting apparatus which can be suitably applied to an image recording apparatus such as an electrostatic color plotter.
2. Description of the Related Art
An image recording apparatus such as a color plotter generally has the following arrangement. An apparatus of this type comprises a recording paper roll, an image recording processing station, a recording paper feed roller, a recording paper take-up roller, and the like. In this arrangement, an extracted portion of rolled recording paper stretched between the recording paper roll and the recording paper take-up roller is reciprocated a plurality of times. During this reciprocation period, a plurality of images of different colors are overlapped on the same image area of the recording paper by means of the image recording processing station, thus obtaining a multicolor image. An apparatus having such an arrangement is disclosed in, e.g., U.S. Pat. No. 4,569,584.
FIG. 1 is a view showing a prior apparatus having the above-described arrangement, which is disclosed in Published Unexamined Japanese Patent Application No. 62-269851 (corresponding U.S. Pat. No. 4,733,270) associated with the prior invention of the present inventor. Referring to FIG. 1, reference numeral 1 denotes a recording paper roll; and 2, an image recording processing station consisting of constituent elements 3 to 8. The constituent element 3 is a multistylus electrostatic recording head; the constituent element 4, a back-surface roller; and the constituent elements 5 to 8, color developing heads of different colors. Reference numeral 10 denotes a recording paper feed roller; 9 and 11, press rollers which are opposed to the roller 10 so as to be in contact therewith; 12, a temporary recording paper take-up unit constituted by a recording paper take-up roller 13, a guide plate 14, a pinch roller 15, a pinch roller guide 16, and the like; 17, a recording paper path switching guide plate having one end pivotally supported by a support shaft 18; and 19, an automatic cutter including a Y cutter 20 for cutting extracted recording paper P in a direction perpendicular to its feed direction, and an X cutter 21 for cutting the recording paper P in a direction parallel to the feed direction.
According to the apparatus shown in FIG. 1, an extracted portion of the rolled recording paper P is reciprocated a plurality of times. During this reciprocation period, an electrostatic latent image is formed by the electrostatic recording head 3, and development for each color is performed by a corresponding one of the developing heads 5 to 8. As a result, a plurality of images of different colors are overlapped in the same image area of the recording paper P.
The recording paper P used in such an apparatus includes paper having a width ranging from about 24 to 44 inches. In order to form images of the respective colors on an image area of such large-sized recording paper with accurate color matching, some type of color misregistration preventing means must be provided. For example, U.S. Pat. No. 4,569,584 discloses a control system using control marks. This control system can correct positional errors in the recording paper feed direction and in the direction perpendicular to the feed direction, and is very effective in prevention of color misregistration.
Color misregistration due to a ramp of recording paper, however, cannot be prevented by using the above-described control system.
A ramp of the recording paper P occurs immediately after new recording paper (new replacement unit or the like) is set to replace the rolled recording paper P. The ramp amount (degree of ramp) is gradually changed every time the recording paper P is reciprocated.
FIGS. 2 and 3 respectively show states of a ramp of the recording paper P. FIG. 2 emphatically shows the posture (degree of ramp) of the rolled recording paper P which is assumed when the recording paper roll 1 is set at a predetermined position and its leading end is wound around the take-up roller 13. As shown in FIG. 2, the edge position of the recording paper P is inclined with respect to the travel direction, as indicated by X. At this time, the leading end of the recording paper P is set at a position deviated to the right in FIG. 2 from a position 0 assumed during stable travel without a ramp by a distance x. If the recording paper P is wound around the take-up roller 13 in this state, the leading end of the recording paper P is wound while spirally deviating from the normal position, as indicated by reference symbol S in FIG. 3. That is, the ramp amount of the recording paper P is gradually decreased toward a stable travel position as the take-up amount of the recording paper P around the take-up roller 13 is increased. The recording paper P finally takes a posture denoted by reference symbol Y in FIG. 3.
When the recording paper P is rewound around the recording paper roll 1, a force directed toward the stable travel position acts on the paper P. For this reason, when the leading end of the paper P is temporarily separated from the take-up roller 13 and is wound therearound again, the paper P takes a posture indicated by reference symbol Z in FIG. 2. The ramp amount of the recording paper P is changed every time the paper P is reciprocated in this manner. Therefore, if images are overlapped on the recording paper P exhibiting such a movement in the above-described manner, color misregistration inevitably occurs, and the quality of an overlapped image is greatly degraded.
Several means for preventing color misregistration due to a ramp of the recording paper P as described above have been proposed.
As a first means, U.S. Pat. No. 4,569,584 described above discloses a technique of preventing color misregistration due to a paper ramp by inclining a recording head in accordance with the ramp state of recording paper.
As a second means, U.S. Pat. No. 3,668,876 discloses a technique of correcting a ramp by inclining the shaft of a recording paper feed roller in accordance with the ramp state of recording paper.
As a third means, Published Unexamined Japanese Patent Application No. 62-215449 discloses a technique of correcting a ramp by adjusting a force acting on recording paper to urge the paper against a recording paper feed roller in accordance with the ramp state of the recording paper.
As a fourth means, Published Unexamined Japanese Patent Application No. 63-112180 discloses a technique of correcting a paper ramp by shifting a recording paper roll in a direction parallel to its axis in accordance with the ramp state of the recording paper.
Each of the first to fourth means, however, is a color misregistration preventing means using a control loop including a mechanical moving system. Therefore, these means have the following problems:
(1) Since these means require a mechanical moving system, the structure of the apparatus is inevitably complicated and increased in size.
(2) Control conditions must be changed for each type of recording paper. Therefore, the control system inevitably has a complicated arrangement.
(3) It is very difficult to find and set stabilization conditions of a control loop. For this reason, overshoot or the like tends to occur in a control operation, and stable, proper control is difficult to perform.
(4) It takes a long period of time to stabilize a control loop. In addition, during this period, a large amount of recording paper is wasted.